1. Field of the Invention
The present invention relates to an image reading apparatus and, more particularly, to an image reading apparatus suitable for a case wherein a transmission image of, e.g., a microfilm, an OHP (overhead projector), or the like is projected onto a screen surface using a projection system, image information is observed on the screen surface and is read by an image reading means, and the read information is printed by, e.g., a digital printer.
2. Related Background Art
There are proposed various image reading apparatuses each of which enlarges and projects a transmission image of, e.g., a microfilm onto a screen surface using a projection system to observe the projected image, reads image information projected onto the screen surface using an image reading means comprising a linear image sensor as a linear light-receiving element sensor, and prints it using a digital printer.
FIG. 1 is a schematic diagram of a conventional image reading apparatus of this type.
In FIG. 1, a transmission image 1 illuminated by an illumination system 11 is enlarged and projected onto the surface of a screen 6 via mirrors 2, 3, and 5 by a projection system 12. Image information projected onto the surface of the screen 6 is observed.
When image information projected onto the surface of the screen 6 is to be copied, an image reading means 7 arranged adjacent to the surface of the screen 6 scans along the surface of the screen 6 in a direction of an arrow 10, so that the image information is photoelectrically read by a linear image sensor. The read image information is printed by, e.g., a digital printer.
In the conventional image reading apparatus shown in FIG. 1, image information projected onto the surface of the screen 6 is photoelectrically read by a light-receiving element 7a of the image reading means 7.
In general, the light-receiving element 7a is optically located in front of the surface of the screen 6 to be separated therefrom by a given distance.
Therefore, image information defocused by a predetermined amount is formed on the surface of the light-receiving element 7a unlike the image information projected onto the surface of the screen 6.
For this reason, when the light-receiving element 7a scans on the surface of the screen 6 to read image information, a magnification error occurs based on the defocus amount, and it is difficult to accurately read image information without causing a magnification error over the entire surface.